Power generation systems often use a finite stored fuel source (e.g., a fuel tank) together with a stored oxidizer source to provide fuel to the power generation system. In such bipropellant rocket systems, it is often desirable to store exact quantities of finite stored fuel source and oxidizer source so that they are exhausted simultaneously during combustion. Considerable time and effort are spent calculating the appropriate quantities of fuel and oxidizer to store on a rocket, measuring consumption of the fuel and oxidizer, and detecting when the fuel and oxidizer are spent. Therefore, a number of power generation systems utilize a stored monopropellant source (or a pre-mixed bipropellant source).
A monopropellant is a single energetic fluid (liquid, gas or a combination of both and sometimes with solid particles entrained) that decomposes to liberate gases and heat. This heated gas can be used to drive other applications (e.g. rocket thrusters, inflation bags, etc). Monopropellants are typically comprised of either a single chemical or, alternatively, mixtures of chemicals that when combined, produce a monopropellant blend. In the monopropellant blend, the constituents most commonly remain well mixed and effectively behave as a single energetic fluid. Many bipropellants (e.g. combination of a fuel and oxidizer such as vaporized fuel and air) when mixed together effectively act as a monopropellant. In one example implementation, the monopropellant is stored as a liquid and decomposes into a hot gas in the presence of an appropriate catalyst, upon introduction of a high-energy spark, or upon introduction of a similar point source ignition mechanism. Example monopropellants include hydrazine, which is often used in spacecraft attitude control jets and hydroxyl ammonium nitrate (HAN). Given the nature of a monopropellant, in an unintentional line ignition of a monopropellant, the monopropellant can act like a fuse and generate combustion waves that can move very rapidly through a fluid conduit or path full of monopropellant. Monopropellants and supply systems for rocket engines and other work producing systems are subject to damage when detonation progresses upstream from a combustion chamber to and through supply lines. Such danger of a flashback from the point of ignition of the monopropellant (or other point along the monopropellant feed line) back to the monopropellant storage tank has prevented the widespread utilization of monopropellants.
Deflagration is a common form of combustion where the flame travels at velocities less than the flame's local speed of sound. Deflagration combustion is most commonly associated with relatively slower burning combustion processes and more commonly seen in lower pressure, lower energy density systems. However, higher energy density systems (such as a high energy density liquid or high-pressure monopropellant gas) with fast chemical decomposition and/or chemical reaction rates may produce a more powerful detonation phenomenon. A detonation is a phenomenon characterized by supersonic flame (which travels at a speed higher than the flame's local speed of sound) front propagation. Usually associated with detonation waves are pressure/temperature spikes and shock waves. The aforementioned conditions can result in a transient phenomenon containing immense power that can be used for destructive or carefully controlled constructive purposes.
Rocket engines, gas generators, power plants, etc., can operate with monopropellants that can have very high gas and/or liquid local combustible energy densities and/or chemical decomposition rates as compared to the energy densities and chemical reaction rates of more conventional bipropellants (e.g., air/fuel mixtures or low-pressure fuel and oxidizer mixtures). Protecting against the detonation wave generated by potential flashback caused in such a system containing monopropellants with very high gas and/or liquid densities is a significant technical challenge.